The present invention relates to a method for producing a measurement program for measuring machining quality in an NC machining process in order to realize an effective NC machining system, and to an NC machining system utilizing the measurement results of the machining quality of the workpieces obtained by using the measurement program produced by this method.
With an NC machine tool, tool movement can be automatically controlled by an input NC program. In addition, in recent years, NC machine tools have come to be widely used in various industrial fields as computerized numerical control machines (CNC machine tools) in combination with advanced technology such as advanced microprocessor, power electronics, or software technology.
Typically, numerical control information such as an NC program includes individual information such as a tool indexing command, a main-spindle speed command, a feed-rate command, a traverse and interpolation command, an auxiliary function command and the like and a working history, and is formed as an NC program so as to be suitable for a machine tool that is a controlled system in machining.
NC programs produced in this manner are used in various machining processes. In order to perform high quality machining, it is necessary to measure the workpiece after a final machining process or at intermediate machining processes and to modify the machining control for the next workpiece or the following machining processes for the same workpiece according to the measured results. Conventionally, measurement is carried out so that sizes of the workpieces are partially measured at intermediate machining processes using simple instruments such as a micrometer or vernier calipers, and then all significant measurements of the workpieces are assessed in a final inspection. When there are any problems concerning the measured results, such a situation is fed back to the NC machining. This feedback of measured results to the machining control is carried out by experienced skilled workmen through oral or memo communication between the workmen. Consequently, with conventional systems it is not possible to automatically feedback the measured results to the machining control in real time.
Moreover, because in conventional simple measurement only limited measurements are made during the machining process,a final inspection is required for precise measurement. Therefore, there are disadvantages in that recognition of the problems is delayed and that the yield of the NC machining is lowered.
In order to solve such problems, an automatic measurement programming method has been proposed in which measurement programs for the finally finished workpieces or for the intermediate processes are prepared in advance, and the measurements are automatically and sequentially carried out during NC machining using an instrument such as a three-dimensional coordinate measuring machine or the like, and the measured results are fed back to the NC machining. According to such art, the measurement itself can quickly and accurately be carried out without relying upon skilled workmen.
However, such a conventional automatic programming requires complicated operations by a CAD/CAM system based on material data, final machined shapes, tool data, and the like. Therefore, there remain problems that the conventional automatic programming cannot be utilized in all NC machining processes, and that a large scale facility is required.This method is therefore rarely utilized only in certain cases where mass production is performed using one NC program.
There are further disadvantages in that a measurement program by an automatic programming is produced based on final shape data of a product, in particular working drawings, and that therefore the measurement program is not optimized for workpiece shapes during intermediate stages of each operation element, working element, or process during execution of an actual NC program.
The expression xe2x80x9cworking elementxe2x80x9d employed herein is defined as a group of a plurality of operation elements for the same machining position of a workpiece. In other words, the operation element is a single machining operation executed by each tool, for example, a single operation such as drilling, milling. Working element refers to a combined operation for completing machining for the same machining position of the workpiece by combining a plurality of operation elements. For example, in the case of machining a threaded hole, the working element is defined as the element composed of three operation elements such as center hole drilling, drilling of a hole before threading, and tapping. In addition, process refers to all of the groups of a series of machining operations to be carried out in the same chucking attitude of a workpiece on a machine tool.
In recent years, it has become common in NC machining to use NC programs that are open and flexible as far as possible. In actual machining, the NC program is often re-edited and modified to pursue an optimum machining method. In addition, NC programs are commonly modularized, or made flexible in order to achieve free modification. As a result, there is such a problem that a conventional machining program simply produced based on a working drawing cannot cope with the respective actual stages of the operation elements, working elements or processes, and cannot be used with advanced NC machine tools.
Furthermore, in recent years, advanced NC machining has come to be performed out not only by a single machine tool, but also by CIM (Computer Integrated Manufacturing) system coordinating a number of machine tools. In such cases, there is also such a problem that a conventional non-flexible measurement program cannot be imparted with learning ability to cope with the application to other machine tools or the application to new machine tools.
In an attempt to deal with such a problem, technology such as disclosed in PCT/JP96/03265 is proposed. However, while many of the problems described above are addressed by that technology, there remains many possible improvements for more efficiently producing a measurement program. The object of the present invention is to provide a new method and system for improving this technology.
A method for producing an NC program according to the present invention in order to achieve the object describe above is characterized in that machining quality information concerning the machining quality after machining a workpiece is written in the NC program. The machining quality information includes information on the tolerance and surface roughness required of the workpiece after machining.
In addition, the NC machining system according to the present invention may comprise the steps of producing a measurement program for measuring machining quality of a workpiece machined using a machine tool by a measuring machine through analyzing the NC program produced according to the method described above; measuring the machining quality of the workpiece using the produced measurement program and the measuring machine; and discriminating the machining quality of the workpiece by comparing the results of the machining quality of the workpiece measured by the measuring machine and the required machining quality information included in the NC program.
Furthermore, the NC machining apparatus according to the present invention may comprise measurement program producing means for producing a measurement program for measuring machining quality of the workpiece machined using a machine tool by a measuring machine through analyzing the NC program for executing a machining control of the machine tool for the workpiece; a measuring machine for measuring the machining quality of the workpiece using the produced measurement program; and discriminating means for discriminating the machining quality of the workpiece by comparing the results of the machining quality of the workpiece measured by the measuring machine and the required machining quality information included in the NC program.